1. Field of the Invention
The present invention relates to a method and an apparatus for monitoring a vehicle rear which perform an image processing for a vehicle rear image picked up by a camera mounted on a vehicle and which displays the thus-processed image on a monitor, as well as a signal processor used in the vehicle rear monitoring apparatus.
2. Description of the Prior Art
Heretofore there has been known a vehicle rear monitoring apparatus which, for the purpose of improving the safety of vehicle operation and assisting a vehicular parking operation, photographs a road surface and the vicinity of a vehicle with use of a single camera mounted on a rear portion of the vehicle and which reverses the picked-up image right and left and then displays it on a monitor.
As an apparatus which applies an image processing to images inputted from plural cameras to reproduce a sense of distance there is known, for example, a vehicle rear monitoring apparatus disclosed in Japanese Patent Publication No. Hei 3 (1991)-99952. In this vehicle rear monitoring apparatus, an image processing is performed for an image picked up by a camera which faces the rear of the vehicle concerned, to effect a change of visual point (perspective change), and a vehicle rear image is displayed on a monitor in a form such that the vehicle concerned is looked down from a virtual visual point positioned substantially just above the vehicle concerned (the visual field from the virtual visual point will hereinafter be referred to as a “top visual field”) (see FIG. 3 in the above publication).
If such an image conversion method as disclosed in Japanese Patent Application No. 2000-271281 is applied to the aforementioned image processing, then by using a virtual visual point having such an angle of depression as looking down obliquely (the visual field from the said virtual visual point will hereinafter be referred to as “oblique visual field”), an image having a sense close to that obtained when a man looks down the vehicle rear obliquely can be displayed on a monitor at a very wide angle of view. In this connection, how the vehicle concerned is to be displayed on the monitor is here considered. In the foregoing vehicle rear monitoring system using a single camera which has already spread widely (a vehicle rear monitoring system wherein an image picked up by a camera is merely reversed right and left without changing a visual point), it is assumed that the rear portion of the vehicle concerned lies on a tower side of the display screen. Therefore, to match this way of display, a method wherein the vehicle concerned is displayed on a lower position of the monitor and the rear of the vehicle is displayed on an upper position of the monitor, is considered preferably because the user does not have a sense of incongruity.
However, in case of monitoring a top visual field as in the vehicle rear monitoring system described in the foregoing publication '952, it is ordinary to display the vehicle concerned on an upper position of the monitor and to display the vehicle rear on a lower position of the monitor because the user is easy intuitively to understand and so on.
For example, therefore, in the case where a monitor display of a top visual field and that of an oblique visual field can be switched from one to the other, or where a monitor display of a top visual field and that of an image picked up by a single camera can be switched from one to the other, and if the position of the vehicle concerned is switched automatically to the upper or lower side in accordance with the display screen, it becomes no longer possible for the user to judge a correlation between the image before and the image after the switching the monitor display, and thus the monitor system is made less significant.
On the other hand, for preventing such confusion of the user, it may be effective to fix the vehicle position to either the upper or the lower side of the monitor irrespective of the display mode on the screen. By so doing, however, there is a fear that the user may have a sense of incongruity for either of the display screens.